This invention relates to abrasive bodies, particularly abrasive bodies which contain abrasive compacts.
Abrasive compacts are well known in the art and consist essentially of a mass of abrasive particles present in an amount of at least 70 percent, preferably 80 to 90 percent, by volume of the compact bonded into a hard conglomerate. Compacts are polycrystalline masses and can replace single large crystals in many applications. The abrasive particles will be diamond or cubic boron nitride.
Diamond compacts will typically contain a second phase uniformly distributed through the diamond mass. The second phase may contain a dominant amount of a catalyst/solvent for diamond synthesis such as cobalt, nickel or iron. Diamond compacts having second phases of this nature will generally not have thermal stability above 700.degree. C.
Diamond abrasive compacts may be used alone or as composite compacts in which event they are backed with a cemented carbide substrate. Composite diamond abrasive compacts wherein the second phase contains a diamond catalyst/solvent are widely used in industry.
Examples of composite diamond abrasive compacts are described in U.S. Pat. No. 3,745,623 and British Patent Specification No. 1,489,130.
Examples of cubic boron nitride compacts are described in U.S. Pat. Nos. 3,743,489 and 4,666,466.
Diamond abrasive compacts of the type described above are thermally sensitive above a temperature of about 700.degree. C. There are, however, described in the literature and in commercial use several diamond abrasive compacts which are thermally stable above 700.degree. C. Examples of such compacts are described in U.S. Pat. Nos. 4,244,380 and 4,534,773 and British Patent No. 2,158,086.
In some applications, particularly for drilling, it is desirable to bond a composite abrasive compact, particularly a composite diamond abrasive compact, to an elongate cemented carbide pin. The product known as a stud cutter is then brazed to the working surface of a drill crown. During this second brazing, weakening of the bond between the composite compact and the pin is known to occur.
Kennametal South African Patent No. 88/5847 describes a method of bonding an elongate cemented carbide tool insert to the steel body of a conical bit. Bonding is achieved by brazing the carbide to the steel. A perforated metal shim is provided between the carbide and the steel and the braze is allowed to flow through the shim. The presence of the shim is said to reduce stresses in the braze joint. It is to be noted that the bonding is between a carbide surface and a steel surface. Further, the braze alloy is allowed to infiltrate the perforated shim and is not pre-formed with the shim.